The first objective of this project is to nvestigate the ultrastructure and physiology of the crustacean stretch receptor. The second objective is to investigate fine structural changes and physiological properties of the newly-formed functional neuromuscular junctions in Xenopus laevis culture. In addition, we will study the correlation between the appearance of acetylcholine sensitivity and the appearance of 11 to 19 nm particles (putative acetylcholine receptors) in freeze-fracture, by using Xenopus embroyonic muscle cells in vitro and in vivo. Methods to be used in these studies will be primarily thin-section electron microscopy, freeze-fracture, and micro-eletrophysiology.